Tiniest Planet Yet Discovered by NASA Outside our Solar System

The tiniest planet beyond our Solar System has been discovered by NASA. The artist's concept depicts the new planet dubbed Kepler-37b. The planet is slightly larger than our moon, measuring about one-third the size of Earth. (Photo : NASA/Ames/JPL-Caltech)

The record for the smallest planet beyond our Solar System has been shattered by astronomers. They've recently unveiled a planet that that's only slightly larger than our moon and speeds around its star in a mere 13 days.

The planet, called Kepler-37b, is what is known as an exoplanet, which means that it exists outside of our Solar System. The planet itself is most likely rocky and is unable to support water due to its closeness to its star; it is located approximately 210 light-years away from Earth in the constellation Lyra.. It may be the smallest, but it certainly isn't the only planet that astronomers found. They also located two other planets rotating the same star, Kepler-37c and Kepler-37d. One is about three-quarters the size of Earth while the other is about twice the size of Earth (See image). Both of them also rotate close enough to their star to make water an impossibility.

The line up compares the smallest known planet to the moon and planets in the solar system. Credit: NASA/Ames/JPL-Caltech

Actually learning the planets measurements, though, was a different process from merely detecting it. The astronomers measured the star that it orbited and then compared the measurements with the actual planet. In this way, they were able to find the approximate size of the tiny planet.

How did astronomers find these planets in the first place, though? They're getting better and better at finding planets in far-flung solar systems. The Kepler space telescope allows them to detect tiny dips in stars' light that happens when planets pass in front of them. Called a transit event, this change in light allows astronomers to detect new planets.

Yet while the Kepler telescope was usually able to detect large planets at first, it wasn't always able to detect smaller ones. In its earliest days, it only found behemoths around the size of Jupiter or Neptune. More recently, it has found planets that are about twice the radius of our planet.

Considering that the latest find is so small, it shows a major technological improvement for the telescope. The telescope itself has been recording data for nearly four years, and signals that would have once been too small to notice have slowly been accumulating, which explains why astronomers are now more likely to see the tinier planets.

In the coming years, astronomers will most likely continue to keep announcing more and more exoplanets that are being discovered. Francois Fressin, co-author of the paper that announced the findings, said in an interview with BBC News, "I understand that people could be bored by these successive announcements, but hundreds or thousands of years from now, this will be remembered as the decade where discovery of other worlds of all kinds has been made possible."